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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Feature Description
The AT1312A/B/C step-up converter drives white *Operating Voltage:2.5V to 6.0V. LEDs with a constant current to provide backlight in *High Operating Frequency: 1MHz cell phones, PDAs, and other hand-held devices. It *High Output Voltage: Up to 16V/23V/28V features allowing series connection of the white LEDs so that the LED currents are identical for *Shutdown Current <1A uniform brightness. An enable input can be pulsed *16V/23V/28V Output Over-Voltage Protection repeatedly to adjust LED's brightness. The fast 1.0 *Digital Dimming Control. MHz current-mode PWM control allows for smaller capacitor and inductor. Fault condition protection *Built-in Cycle-by Cycle Current-Limiting. uses cycle-by-cycle current limiting to sense *Built-in Soft-Start Function. maximum inductor current, thermal protection and *0.2V Low Reference Voltage over-voltage protection. Also included soft-start eliminates inrush current during start-up. The 0.2V *Tiny SOT-26 Package low reference voltage minimized the power loss across the current-setting resistor.
Application
* LED Module * Compact Back Light Module * Constant Current Source
The AT1312A/B/C is available in 6-pin SOT-26 packages.
Block Diagram
Aimtron reserves the right without notice to change this circuitry and specifications.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Pin Configuration
SOT-25 (TOP VIEW) VIN OVP EN 6 312 5 4
A:1312AX B:1312BX C:1312CX
1 LX
2
3
GND FB
Ordering Information
Current Limit AT1312AX SOT-26 400mA AT1312AX_GRE SOT-26, Green 400mA AT1312BX SOT-26 AT1312BX_GRE SOT-26, Green AT1312CX SOT-26 AT1312CX_GRE SOT-26, Green 300mA 300mA 200mA 200mA Part number Package OVP Protection 28V 28V 23V 23V 16V 16V Marking Date Code ,Date Code with one bottom line Date Code ,Date Code with one bottom line Date Code ,Date Code with one bottom line
: Date Code *For more marking information, contact our sales representative directly
Pin Description
Pin N0. 1 2 3 4 5 6 Symbol LX GND FB EN OVP VIN I/O I P I I I P Description Step-up Regulator N-MOS Drain. Place output diode and inductor. Ground Step-Up Regulator Feedback Input. Connect a sense resistor from FB to ground. Enable and Dimming Control Input. LED brightness and IC shutdown are controlled by the voltage on EN. Driving low for longer than 4ms to shutdown the IC. Over-voltage protection input. Connect to the output. Power supply.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Absolute Maximum Ratings*1
Parameter VIN voltage LX , OVP voltage EN , FB to GND Switch Current (ILX) Continuous power dissipation (SOT-26 Ta=+25 C) Operating Junction Temperature Range Lead Temperature (Soldering 5 sec) Storage Temperature Package Thermal Resistance (JA) ESD Susceptibility*2 HBM MM
O
Rated Value -0.3 to +6.5 -0.3 to +28 -0.3 to +6.5 0.6 0.35 -30 to 85 260 -65 to 125 250 2 200
Unit V V V A W /W KV V
1. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2. Device are ESD sensitive. Handling precaution recommended. The Human Body model is a 100pF capacitor discharged through a 1.5K resistor into each pin.
Recommended Operation Conditions
Parameter Power supply voltage Operating temperature Symbol Min. VIN Top 2.5 -20 Values Typ. +25 Max. 6.0 +85 Unit V
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Electrical Characteristics
(VIN=2.5V, Ta=+25, unless otherwise noted)
Parameter Operating V IN Range Under Voltage Thershold Switch- Off Input Current Shutdown Current Feedback Reference FB Input Bias Current Over-voltage Threshold Over-voltage Hysteresis OVP Leakage Current Output Voltage Line Regulation Switching Frequency Maximum Duty Soft-Start charging time
Symbol VIN UVLO IIN1 IIN3 VFB IFB VOVP
Test Condition VIN input Voltage VIN falling, 100mV hysteresis No Switching EN=0V VFB =0.2V VOUT Rising (AT1312A) VOUT Rising (AT1312B) VOUT Rising (AT1312C) EN=0V 2.5V< VIN <6.0V
Min. 2.5 2.1 0.190 0.05
Typ. Max. Units 2.2 100 0.2 28 23 16 2 0.1 1 90 0.5 400 300 200 0.3 4 120 6.0 2.3 120 1 0.210 1 25 18 1 5 1 0.8 5 5 V V A A V A V V V V A % MHz % ms mA mA mA A A V V ms ms ms
IOVP fOSC DMAX tSS
Switching Current Limit
ILX
LX ON Resistance LX Leakage Current EN Input Current EN Input Level EN low Shutdown Delay EN Low Cycle Time EN High Cycle Time Thermal Shutdown
RLX ILeakage IEN VIH VIL tCYCL tCYCH
VIN=3.0V,duty cycle=80% , (AT1312A) VIN=3.0V,duty cycle=80% , (AT1312B) VIN=3.0V,duty cycle=80% , (AT1312C) VIN =2.5V, ILX =200mA VLX =16V/23V/28V, EN=0V EN=5V 0.1V hysteresis
2.0 -
*1 *1
0.05 0.05 -
*1: tCYCL and tCYCH are included rising time and falling time of PWM signal.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Typical Characteristics
Conversion Efficiency L:SR0302 D:RB501-40
90 90 88 85 86 84 Efficiency (%)
Efficiency (%)
Efficiency vs. Vin (3 LED) L:SR0302 D:RB501-40
80 75
6 L E D s, L = 2 2 u H , V in = 3 V
82 80 78 76 74 72 70 2 3 4
Vin (V)
Io=20 m A, L =22u H Io=20 m A, L =10u H Io = 2 0 m A,L = 6.8 u H Io = 2 0 m A,L = 4.7 u H
70
4 L E D s, L = 2 2 u H , V in = 3 V 3 L E D s, L = 2 2 u H , V in = 3 V
65 0 5 10 LED CURRENT(mA) 15 20
5
6
Efficiency vs. Vin (4 LED) L:SR0302 D:RB501-40
90 88 86 84 82 80 78 76 74 72 70 2 3 4
Vin (V)
Efficiency vs. Vin (6 LED) L:SR0302 D:RB501-40 90 88 86 84 82 80 78 76 74 72 70 2 3 4
Vin (V)
Io=20mA, Io=20mA,
L=22uH L=10uH
Efficiency (%)
Efficiency (%)
Io=20mA, L=22uH Io=20mA, L=10uH Io=20mA,L=6.8uH Io=20mA,L=4.7uH
Io=20mA, L=6.8uH Io=20mA,L=4.7u
H5
6
5
6
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver
Efficiency vs. Vin (6 LED) L:SR0302 D:RB501-40
90 88 86 84
Efficiency (%) Efficiency (%)
Efficiency vs. Vin (4 LED) L:SR0302 D:RB501-40
90 88 86 84 82 80 78
Io=10 m A, L =22u H
82 80 78 76 74 72 70 2 3 4
Vin (V)
Io=10 m A, Io=10 m A, L=22uH L=10uH
76
Io=10 m A, L =10u H
Io = 1 0 m A, L = 6.8 u H Io = 1 0 m A, L = 4.7 u H
74 72 70 2 3 4
Vin (V)
Io = 1 0 m A,L = 6.8 u H Io = 1 0 m A,L = 4.7 u H
5
6
5
6
Ch1:LX
Ch2:ILX
Ch3:Vo
Ch1:LX :10V/div , Ch2:ILX: 200mA/div, Ch3: Vo :100mV/div ,0.2uS/div Switching Transient Waveform
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver
Ch1:FB
Ch2:EN
Ch1:FB : 200mV/div , Ch2:ENABLE: 2V/div ,0.2mS/div PWM Dimming Control Using the EN Pin
Ch1:IIN
Ch2:FB
Ch3:EN
Ch1:IIN : 200mA/div , Ch2:FB: 100mV/div , Ch3:ENABLE:2V/div ,0.5mS/div Start-Up Waveform
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Application Circuit
Use the tantalum capacitor to eliminate inductor noise on output terminal when you want to control dimming
function.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver
Prevent Emission Caused by White LEDs Leakage
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Function Description The AT1312 series are high efficiency and constant current DC-DC converter IC which is designed primarily for use in LED module applications. The output voltage of the step-up converter can be set from Vin to 16V/23V/28V with external sense resistor. The device suits to drive series-connected LEDs and provides even illumination by sourcing the same output current through each LED. AT1312 series also consists of a logic shutdown, cycle-by-cycle current-limited, soft-start functions. Logic control input or PWM duty cycle control allows easy adjustment of LEDs brightness and on/off control. The average LED current is proportional to the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1KHz. The boost converter operates in current-mode PWM and a constant frequency of 1.0 MHz. Depending on duty cycle of each switching cycle can regulate output voltage. On the rising edge of the internal clock, the control and driver logic block sets internal flip-flop when the output voltage is too low, which turns on the N-MOS. The external inductor current ramps up linearly, storing energy in a magnetic filed. Once peak current of inductor over trans-conductance output level, the N-MOS turns off, the flip-flop resets, and external schottky diode turns on. This forces the current through the inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor and LEDs. To reduce external components, the device will be built-in internal loop compensation. Enable Control Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any voltage less than 0.7V and sustain the level over 4ms will completely turn off the regulator. In this state, current drain from the input supply is less than 1uA, the internal reference, error amplifier, comparators, and biasing circuitry turn off. If holding time of low level is less than 3ms on this pin, then the device only shutdown driver logic block. Dimming Control Digital logic of EN also provides LEDs brightness control by applying a PWM signal on EN pin. With this way, the LEDs operate with either zero or full current. The average LED current is proportional to the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1KHz. Output current is given by:
I LED = 200mV x TON - PWM RSENSE x TS - PWM
Where: TON-PWM : On time of PWM signal TS-PWM : A cycle time of PWM signal If dimming control is not required , EN works as a simple on/off control. Drive EN
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver high to enable the device , or drive EN low for shutdown. Soft-Start Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during power-up to reduce input surge currents. As the internal current source charges the internal soft-start capacitor, the peak N-MOS current is limited by the voltage on the capacitor. In another story, when toggle or a logic-level transition on EN pin from low to high, soft-start function must work to enable constant current charging internal capacitor. When soft-start process has finished or appeared falling edge of PWM signal on EN pin, soft-start capacitor must be discharged to ground level. Cycle-by-Cycle Over-Current Protection The AT1312 series provides cycle-by-cycle over-current protection. Current limit is accomplished using a separate dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS in event that the current of flowing N-MOS is greater than the current limit value. The current-limit feature protection against a hard short or over-current fault at the output. Over-Voltage Protection If VOUT is above 16V/23V/28V( for AT1312A/B/C) or LEDs are disconnected from the circuit, the FB pin is similar to pull down to ground with a sense resistor. This will cause N-MOS to switch with a maximum duty cycle and come out output over-voltage. This may cause the LX pin voltage to exceed its maximum voltage rating to damage built-in N-MOS. In the state, the OVP protection circuitry stops the internal N-MOS. When VOUT falls below 14V/21V/26V, IC will automatically recover normal operation. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the AT1312 series. When the junction temperature exceeds Tj=130 , a thermal sensor activates the thermal protection, which shuts down the IC, allowing the IC to cool. Once the device cools down by 10 , IC will automatically recover normal operation. For continuous operation , do not exceed the absolute maximum junction-temperature rating of Tj=120 . Power dissipation consideration The AT1312 series maximum power dissipation depends on the thermal resistance of the IC package and circuit board, the temperature difference between the die junction and ambient air, and the rate of any airflow. The power dissipation in the device depends on the operating conditions of the regulator. In continuous condition, the step-up converter power dissipated internally across the internal N-MOS can be approximated by :
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver
Pboost = [( I O x VO 2 1 Vin x D 2 ) ] x RDS (ON ) x D )+ ( Vin 12 f OSC x L
where IO : It is the load current. fOSC : It is a switching frequency.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Application Information External components of boost converter can be designed by performing simple calculations. Boost inductor Inductor selection depends on input voltage, output voltage, maximum output current, switching frequency and availability of inductor values. The following boost circuit equations are useful in choosing the inductor values based on the application. They allow the trading of peak current and inductor value while allowing for consideration of component availability and cost. The peak inductor current is given by:
I Lpeak = I LAVG + I LAVG = IO 1- D
I L 2
where: IL is the inductor peak-to-peak current ripple and is decided by: V D I L = in x L f OSC D is the MOSFET turn on ratio and is decided by: V -V in D= O VO fOSC is the switching frequency. The inductor should be chosen to be able to handle this current and inductor saturation current rating should be greater than IPEAK.
Diode selection The output diode has average current of IO, and peak current the same as the inductor's peak current and a voltage rating at least 1.5 times the output voltage. Schottky diode is recommended and it should be able to handle those current. Output Capacitor The AT1312 series are specially compensated to be stable with capacitors which have a worst- case minimum value of 1uF at the particular VOUT being set. Output ripple voltage requirements also determine the minimum value and type of capacitors. Output ripple voltage consists of two components the voltage drop caused by the switching current through the ESR of the output capacitor and the charging and discharging of the output capacitor: V - Vin IO V RIPPLE = I LPEAK x ESR + O x VO C OUT x f OSC For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the output capacitor.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver
PCB layout guidelines Careful printed circuit layout is extremely important to avoid causing parasitical capacitance and line inductance. The following layout guidelines are recommended to achieve optimum performance. * Please the boost converter diode and inductor close to the LX pin and no via. Keep traces short, direct, and wide. * Please ceramic bypass capacitors near the input/output pin. * Locate all feedback sense resistors as close to the feedback pins as possible. * The ground connections of VIN and VOUT should be as close together as possible.
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Small Outline SOT-26
b
e
E
e1 D A A2 A1
C r E1 L
SYMBOL A A1 A2 b C D E E1 L e e1 r
INCHES MIN 0.035 0.000 0.035 0.010 0.003 0.110 0.102 0.059 0.014 00 0.037ref 0.075ref MAX 0.057 0.006 0.051 0.020 0.008 0.122 0.118 0.069 0.022 100
MILLIMETERS MIN MAX 0.90 1.45 0.00 0.15 0.90 1.30 0.25 0.50 0.08 0.20 2.80 3.10 2.60 3.00 1.50 1.75 0.35 0.55 0.95ref 1.90ref 00 100
NOTES -
-
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AT1312A/B/C
Preliminary Product Information High Efficiency, Constant Current White-LEDs Driver Reflow Profiles
Profile Feature
Average ramp-up rate (TL to TP) Preheat -Temperature Min(Tsmin) -Temperature Max (Tsmax) -Time (min to max)(ts) Tsmax to TL -Ramp-up Rate Time maintained above: -Temperature (TL) -Time (tL) Peak Temperature(TP) Time within 5C of actual Peak Temperature (tP) Ramp-down Rate Time 25C to Peak Temperature
Sn-Pb Eutectic Assembly Large Body Small Body Pkg. thickness Pkg. thickness <2.5mm or Pkg. 2.5mm or Pkg. 3 volume <350mm3 volume 350mm 3C/second max.
Pb-Free Assembly Large Body Small Body Pkg. thickness Pkg. thickness 2.5mm or Pkg. 2.5mm or Pkg. 3 volume 350mm volume 350mm3 3C/second max.
100C 150C 60-120 seconds
150C 200C 60-180 seconds 3C/second max.
183C 60-150 seconds 225+0/-5C 10-30 seconds 240+0/-5C 10-30 seconds
217C 60-150 seconds 245+0/-5C 10-30 seconds 250+0/-5C 20-40 seconds
6C/second max. 6 minutes max.
3C/second max. 8 minutes max.
*All temperatures refer to topside of the package, measured on the package body surface.
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